1. Field of the Invention
The present invention relates to a specimen testing element, a specimen information obtaining method and a specimen testing apparatus for obtaining information on a specimen typically by analyzing the physical properties of the specimen by means of an electromagnetic wave.
2. Description of the Related Art
Non-destructive testing techniques utilizing a high frequency electromagnetic wave with an appropriate band in the frequency range extending from millimeter waves to tera-hertz waves (30 GHz to 30 THz) (to be also referred to as a tera-hertz wave hereinafter) have been developed in recent years. It has been known that absorbable rays capable of being absorbed by various substances including bio molecules are found in the frequency range of tera-hertz wave. Harmless imaging techniques that utilize electromagnetic waves of the above cited frequency zone for see-through examination instruments instead of X-rays are available. Spectral techniques for determining the absorption spectrum and the complex dielectric constant in the inside of a substance to look into the coupled condition of molecules are also available. Techniques for analyzing bio molecules and those for evaluating the carrier density and mobility that utilize electromagnetic waves of the above cited frequency zone are also expected.
An object testing apparatus that utilizes a tera-hertz wave and has a configuration as illustrated in FIG. 10 of the accompanying drawings is known (Japanese Patent Application Laid-Open No. H08-320254). The testing apparatus disclosed in the above-cited patent document is designed to irradiate a tera-hertz wave that propagates in space onto an object 10 and observe the component material or materials of the object by means of the change in the propagation state of the wave transmitted through the object. Thus, a penetrative image of the inside of the object can be obtained by two-dimensionally scanning the object.
With the above-described technique, a tera-hertz wave is made to propagate by way of space. However, it is popularly known that a tera-hertz wave propagates through many transmission paths that are being used to propagate high frequency electromagnetic wave signals. Therefore, it is possible to control the propagation state of a tera-hertz wave like any other high frequency electromagnetic waves. For the purpose of controlling the propagation state of a tera-hertz wave, there has been proposed a method of arranging a first electrode 11 and a second electrode 12 on a substrate 13 to form a transmission path and periodically arranging dielectric bodies 14 having different dielectric constants on a part of the a dielectric substrate 13 as shown in FIG. 11 of the accompanying drawings (Japanese Patent Application Laid-Open No. 2004-120260). A photonic band gap is formed as the dielectric constants are changed with lattice gap d and period a so that it is possible to add a sort of resonance structure to the transmission path and filter a part of the signal component of the high frequency electromagnetic wave propagating through the transmission path.
A device illustrated in FIG. 12 of the accompanying drawings is designed to couple a tera-hertz wave onto a transmission path having an optical switch region 21 and a filter region 22 so as to apply it to a DNA sensor (Appl. Phys. Lett., Vol. 80, No. 1, p154-p156, 2002). The coupling state of the spiral structure of DNA is detected from the change in the propagation state of the tera-hertz wave propagating through the transmission path.
Generally, a tera-hertz wave is strongly absorbed by water. Japanese Patent Application Laid-Open No. H08-320254 discloses an arrangement for detecting a tera-hertz wave transmitted through a specimen for the purpose of detecting the physical properties of the specimen. However, as a tera-hertz wave is propagated through the atmosphere, it is attenuated to a large extent by the moisture in the atmosphere. To alleviate the influence of the atmosphere, a technique of adjusting the atmosphere is required for a region surrounding the propagation path of the tera-hertz wave. Then, the entire arrangement is forced to involve large dimensions due to the means for adjusting the atmosphere. Additionally, when the specimen itself shows a strong absorption characteristic relative to tera-hertz waves, the output of the transmitted tera-hertz wave is weakened due to the absorption by the specimen. Such a problem may be avoided when the specimen is made to show a profile of a thin film to effectively reduce the extent to which the tera-hertz wave is absorbed by the specimen. However, such an arrangement will degrade the detection sensitivity because the part of the specimen that interacts with the tera-hertz wave (the quantity of the specimen in the tera-hertz wave transmitting direction) is also reduced. Additionally, an additional step of processing the specimen will be required.
When a transmission path as disclosed in Japanese Patent Application Laid-Open No. 2004-120260 is used, the high frequency electromagnetic wave that propagates through the transmission path concentrates in the dielectric substrate that provides the transmission path, although the extent of concentration may vary depending on the profile of the transmission path. Therefore, when such an arrangement is applied to transmission of a tera-hertz wave, it may not be possible to suppress the attenuation of the signal due to the atmosphere because the tera-hertz wave concentrates in the substrate. However, no technique has been disclosed to date for controlling the propagation state of the tera-hertz wave in a transmission path by using a band gap formed according to Japanese Patent Application Laid-Open No. 2004-12060 and applying the technique to testing a specimen.
The DNA sensor disclosed in Appl. Phys. Lett., Vol. 80, No. 1, p154-p156, 2002 employs a micro-strip line 23 as transmission path. Then, the DNA, or the specimen 24, is dropped on a conductor of the micro-strip line. The tera-hertz wave that propagates through the transmission path concentrates in the dielectric substrate 25 that is sandwiched between the two conductors of the micro-strip line. Therefore, only the tiny electromagnetic wave leaking out to the vicinity of the conductors is used as a tera-hertz wave for sensing the specimen. In short, the efficiency of utilization of a tera-hertz wave is low for the detecting operation. Thus, there is a demand for specimen testing elements showing a high efficiency of utilization of a tera-hertz wave.